Ferguson aiming to get balance right
United, who are second domestically, beat Braga 3-2 in the Champions League on Tuesday after trailing 2-0 inside the first 20 minutes to top Group H with maximum points from their three games.
Javier Hernandez, who has often been overlooked this season despite scoring three goals from four starts, netted twice to rescue the win and the Mexican has given manager Ferguson a selection dilemma for the clash at Stamford Bridge.
"The boy is improving all the time," Ferguson told reporters. "He is fantastic in training and he's always practising.
"His goal ratio for us is fantastic. For his second goal he bends around the back of the defender. It is a great ball in from Tom Cleverley but his movement is terrific. He's given me a problem - but that's a good thing."
With Robin van Persie, Wayne Rooney and Danny Welbeck also vying for spots up front, United look spoilt for choice against a Chelsea side who have their own problems.
Among them is the continuing absence of skipper John Terry, serving the second of his four-match English ban for racially abusing Queens Park Rangers defender Anton Ferdinand last year.
They could also be without midfielder Frank Lampard, who was having a scan on the injured calf that caused him to limp out of Chelsea's 2-1 Champions League defeat at Shakhtar Donetsk after only 18 minutes on Tuesday.
The weekend's other high profile match is fourth-placed Everton facing Liverpool in the first Merseyside derby of the season at Goodison Park on Sunday.
Champions and third-placed Manchester City are at home to Swansea City on Saturday and fifth-placed Tottenham Hotspur visit lowly Southampton on Sunday.
Despite it still being relatively early in the campaign, Chelsea's meeting with United could have a significant bearing on the outcome of this season's title race.
Chelsea's superb 4-2 come-from-behind win at Spurs on Sunday was their seventh victory out of eight matches this term and they host United as one of the only two unbeaten sides in the league, with City being the others.
Chelsea lead the table with 22 points, followed by United and City on 18, Everton on 15 and Spurs leading a trio of clubs on 14.
United, though, have not lost any of their last five games against Chelsea and their meeting in the league there last season was a classic as they came back from 3-0 down to draw 3-3.
That score-line encapsulates their current problem - potent in attack but weak at the back.
United fell behind for the eighth time in 12 games this season against Portugal's Braga and Ferguson is perplexed.
"I can't understand our defending," he said. "I can't get to the bottom of it. We certainly make it difficult for ourselves. If you analyse the goals we are conceding they are all different types.
"It is difficult to put my finger on it and it certainly doesn't give us a good start to g